You went from an unprovable absolute claim to providing anecdotal evidence. I'm not saying you're wrong... just that what you've said so far doesn't convince me that "copyright should not be effectively forever" or that "50 years after they are dead" is "effectively forever".
This is by no means my area of expertise, but I'll give you an (probably unoriginal) example. Let's say an artist creates something at age 30. He could use some extra money at age 70. Wouldn't he be able to sell the rights for more to someone who the law will allow to retain those rights for more years after this artist has died?